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nir/repair_ssa: Repair dominance for unreachable blocks 

NIR currently assumes that unreachable blocks are trivially dominated by
everything.  However, when considering well-formed SSA, there is no path
from any block to an unreachable block.  Therefore, we can break any
use-def chains where the use is in an unreachable block.  This removes
any dependencies on code created by uses in unreachable blocks and lets
DCE do a better job of cleaning it up.

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
This commit is contained in:
Jason Ekstrand 2019-09-02 12:54:31 -05:00
parent f81a2623d8
commit a3268599f3
1 changed files with 8 additions and 4 deletions
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12
src/compiler/nir/nir_repair_ssa.c
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@ -71,7 +71,8 @@ repair_ssa_def(nir_ssa_def *def, void *void_state)
bool is_valid = true;
nir_foreach_use(src, def) {
if (!nir_block_dominates(def->parent_instr->block, get_src_block(src))) {
if (nir_block_is_unreachable(get_src_block(src)) ||
!nir_block_dominates(def->parent_instr->block, get_src_block(src))) {
is_valid = false;
break;
}
@ -80,7 +81,8 @@ repair_ssa_def(nir_ssa_def *def, void *void_state)
nir_foreach_if_use(src, def) {
nir_block *block_before_if =
nir_cf_node_as_block(nir_cf_node_prev(&src->parent_if->cf_node));
if (!nir_block_dominates(def->parent_instr->block, block_before_if)) {
if (nir_block_is_unreachable(block_before_if) ||
!nir_block_dominates(def->parent_instr->block, block_before_if)) {
is_valid = false;
break;
}
@ -101,7 +103,8 @@ repair_ssa_def(nir_ssa_def *def, void *void_state)
nir_foreach_use_safe(src, def) {
nir_block *src_block = get_src_block(src);
if (!nir_block_dominates(def->parent_instr->block, src_block)) {
if (nir_block_is_unreachable(src_block) ||
!nir_block_dominates(def->parent_instr->block, src_block)) {
nir_instr_rewrite_src(src->parent_instr, src, nir_src_for_ssa(
nir_phi_builder_value_get_block_def(val, src_block)));
}
@ -110,7 +113,8 @@ repair_ssa_def(nir_ssa_def *def, void *void_state)
nir_foreach_if_use_safe(src, def) {
nir_block *block_before_if =
nir_cf_node_as_block(nir_cf_node_prev(&src->parent_if->cf_node));
if (!nir_block_dominates(def->parent_instr->block, block_before_if)) {
if (nir_block_is_unreachable(block_before_if) ||
!nir_block_dominates(def->parent_instr->block, block_before_if)) {
nir_if_rewrite_condition(src->parent_if, nir_src_for_ssa(
nir_phi_builder_value_get_block_def(val, block_before_if)));
}